1. Field of the Invention
This invention relates to a circuit and a method for producing a very low voltage power supply utilizing the band gap technology.
More particularly this invention relates to a band gap circuit which can operate at a voltage as low as 1.2 volts using a low power process.
2. Description of Related Art
FIG. 1 illustrates a conventional current band gap reference circuit. Devices 120, 130 and 140 are bipolar transistors with their bases and collectors shorted together. This results in the creation of PN diodes 120, 130, 140 whose N side is connected to ground 110 in FIG. 1. There are three p-channel MOSFETs in FIG. 1. They are devices 190, 155 and 195. The drains of these devices are connected to the supply voltage, VDD 100. These devices are used as current sources and current mirrors. Devices 170 and 180 are n-channel MOSFETs. They are also used in the current reference and current mirror function of this circuit. Similarly, resistor R1150 is used to bias the current reference formed by devices 155, 180 and 130. Resistor R2160 is used to bias the voltage reference formed by devices 195 and 140.
The voltage at node xe2x80x98Axe2x80x99 175 has to be larger than Vtn+Vbe where Vtn is the threshold of the NMOS (n-channel metal oxide field effect transistor) 170 in FIG. 1 and where Vbe is the base to emitter voltage drop of bipolar transistor connected as a diode 120. In a low power semiconductor manufacturing process, Vtn+Vbe could be close to 1.6 volts at a low temperature condition. This higher voltage level makes this circuit unsuitable for the low voltage, low power applications of today.
U.S. Pat. No. 5,686,823 (Rapp) xe2x80x9cBandgap Voltage Reference Circuitxe2x80x9d describes a circuit comprising a feedback controlled current mirror, a band gap voltage generator, and a voltage comparator. This bandgap voltage reference circuit generates a bandgap voltage reference and a current mirror reference while operating over a wide power supply voltage range and down to very low power supply voltage levels.
U.S. Pat. No. 6,075,407 (Doyle) xe2x80x9cLow Power Digital CMOS Compatible Bandgap Referencexe2x80x9d describes a band gap reference that is compatible with a low voltage CMOS process. It utilizes ratioed current mirrors to provide loop gain and to minimize the offset sensitivity of the loop amplifier.
U.S. Pat. No. 6,150,872 (McNeil et al.) xe2x80x9cCMOS Bandgap Voltage Referencexe2x80x9d shows a band gap voltage reference circuit for 0.35 micron, 3-volt CMOS technology. This circuit operates in an essentially temperature independent manner and having low supply voltages.
It is the objective of this invention to provide a circuit and a method for producing a very low voltage power supply utilizing the band gap technology.
It is further an object of this invention to produce a band gap circuit which can operate at a voltage as low as 1.2 volts using a low power process.
The objects of this invention are achieved by a low voltage supply band gap circuit made up of a PN diode xe2x80x98Axe2x80x99 whose N side is connected to ground and whose P side is connected to the plus input of a differential voltage comparator, a PN diode xe2x80x98Bxe2x80x99 whose N side is connected to ground and whose P side is connected to one node of a series resistor. The series resistor whose other node is connected to the minus input of a differential voltage comparator, differential voltage comparator, a resistor xe2x80x98Cxe2x80x99 which is connected to the output of said differential voltage comparator and to the plus input of said differential voltage comparator, a resistor xe2x80x98Dxe2x80x99 which is connected to the output of said differential voltage comparator and to the minus input of said differential voltage comparator.
The objects of this invention are further achieved by a a method of providing a low voltage supply band gap circuit made up of the steps of connecting a PN diode xe2x80x98Axe2x80x99 whose N side is connected to ground and whose P side is connected to the plus input of a differential voltage comparator, connecting a PN diode xe2x80x98Bxe2x80x99 whose N side is connected to ground and whose P side is connected to one node of a series resistor, and connecting said series resistor whose other node is connected to the minus input of a differential voltage comparator. In addition, the method steps include connecting the differential voltage comparator, connecting a resistor xe2x80x98Cxe2x80x99 which is connected to the output of the differential voltage comparator and to the plus input of the differential voltage comparator, and connecting a resistor xe2x80x98Dxe2x80x99 which is connected to the output of the differential voltage comparator and to the minus input of the differential voltage comparator.